The present invention relates to data storage systems utilizing an optical disk drive. More specifically, the present invention relates to an apparatus and system which optimizes the read focus offset in order to provide optimal focus for a read head in an optical disk drive.
In optical data storage systems, it is necessary to read out data from a data storage media utilizing an optical system. This optical system will detect variations or marks in the data storage media (e.g. an optical disk). These marks are written to the storage media in a meaningful manner and make up the stored data such that accurate retrieval is critical in order to reproduce the stored data.
As expected, the optical system typically includes various lenses and positioning devices which cooperate with one another to provide focusing on the data storage media. The optical characteristics of this system will often change over time thus causing variations in the system operation. These changes can result from a large number of things. Changes in temperature can cause related changes in optical properties, all of which dramatically affect the operation of the system. Further, the optical elements are typically mechanically positioned and aligned. This alignment and positioning can vary as the disk drive itself encounters shock and vibration. All of these misalignments affect the focusing of the read out system, and ultimately affect the performance of the disk drive.
Typically, read out systems include mechanisms which allow some offset to be injected into the focusing control. Often, focusing is controlled by a servo which will drive a focus motor and appropriately position the focusing lens. As is well known, an offset can easily be introduced into this servo system in order to vary the focus operations. Due to the circumstances outlined above, it is necessary to periodically check the focusing operation and insure that optimum focusing parameters are being used.
In addition to variations in the alignment of the focusing system, the actual storage media may not be consistent. Substrate thicknesses in the optical media often change from disk to disk. This requires that the read focus be optimized every time a disk is changed.
While it is possible to optimize the read focus characteristics of the read out system in all appropriate circumstances, lengthy calibration procedures increase the overall spin-up time. As expected, speed is critical in data retrieval systems so a lengthy spin-up time is undesired.
Various methodologies have been used to optimize read focus offset. U.S. Pat. No. 5,574,706 entitled xe2x80x9cFocus Offset Optimization For Reading Optically-Recorded Dataxe2x80x9d describes one such methodology wherein both control marks and reference data marks are recorded in each frame when the disk is initially written. The recorded reference data marks are placed no farther apart than the smallest distance between two successive data marks which must be resolved as a blank space or zero during the read out process. Analyzing the signals produced when reading out these signals, and insuring that the distance between marks can be resolved allows for optimum read focus. This method requires the placement of these reference data marks be recorded in each frame however, thus adding to the complexity of the storage frames. Additionally, a relatively small number of marks are placed in each frame, thus the accuracy of any amplitude measurements is not optimum. Further, high speed focus optimization is not best accomplished using this method.
Further systems have used isolated data sectors which are continually read at different read focus offset levels. This process however is quite time consuming as it requires the same data sector to be read multiple times. Using this methodology, the same data sector is read in order to ensure that variations in media quality and signal characteristics are accounted for. As can be appreciated, however, this process is time consuming. In order to read the same data sector, one complete revolution is required between each reading cycle. Consequently, if samples are to be taken at 30 different focus offset levels, at least 30 revolutions of the disk are required.
It is beneficial to develop a system and process for efficiently optimizing the read focus of an optical storage system. Such an optimum system would be fast, efficient, and would utilize only a small amount of disk space.
The present invention provides a system and method for read focus optimization which is both efficient and accurate. Further, read focus optimization can be accomplished fairly quickly, thus avoiding long spin up time period.
Prior to the actual process of read focus optimization, the data storage media or disk of the present invention is prewritten with three tracks of data specifically configured for the read focus optimization function. These prewritten tracks are placed at or near the middle radius of the disk, as this area is more representative of the user area than other portions of the disk.
The prewritten tracks of data are made up of data patterns which are chosen to simplify the read focus optimization process. The specific patterns are predominantly or exclusively made up of 3T data patterns of the RLL 1, 7 Code. By using this specific pattern, a focus offset can be determined which provides the maximum peak to peak amplitude when the 3T pattern is read out. Alternatively, the specific data pattern could be predominantly or exclusively a 2T pattern, or some other predetermined data pattern, including a combination of the 3T and 2T patterns.
In order to provide realistic conditions, three parallel tracks of data are written at the center radius, with only the center track including the predetermined data pattern. The two adjacent tracks can be written with any data pattern in order to create interference (cross talk) as is typically with user data. When the data is read for purposes of focus optimization however, only the center track is utilized.
In order to determine the optimum read focus, a specially tailored read function is carried out. In this read process, the above referenced center track of pre-recorded data is read out from the storage media in a specific manner. Also, rather than simply decoding this data and providing decoded data to the data buffer, peak to peak amplitude data is provided. The transferred amplitude data is preconditioned over a few channel bit samples in order to reduce the effects of system noise and media defects.
When reading out this predetermined data pattern, variations in the read focus are made. As is well known, the focus motor includes a servo control. Variations in read focus is accomplished by injecting offsets into this servo control at various points throughout the read process. More specifically, the focus offset is varied in a predetermined manner so that predetermined offsets are used in various sectors. In one embodiment of the present invention, the read focus offset starts at a maximum value and is decremented through a predetermined range. This predetermined range is established by factory default settings established by the manufacturer. After all the data is collected, an average 3T amplitude can then be calculated for each data sector.
In order to quickly perform read focus optimization, the read function actually utilizes two separate read passes. In the first pass no variable read focus offset is used. In the second pass, the same track is read while the offset is varied as mentioned above. Based on these two read passes, an amplitude variation can then be determined for each data sector. Specifically, the 3T peak to peak amplitude from the first pass is compared with the 3T peak to peak amplitude from the second pass for each data sector. The data sector with the largest positive difference is determined to have the optimal focus offset, and provides an optimum offset setting for the read focus servo system. This focus offset can then be used when user data is read. This process is efficiently carried out as only two revolutions of the disk are required.
As can be seen from the details outlined above, the system and process of the present invention accomplishes read focus optimization utilizing only three data tracks in the center of the optical disk. Consequently, the remainder of the area is available for user data writing. This provides for efficient use of the data media. Also, the read focus optimization process can be quickly carried out, thus reducing the initialization or spin-up time required for the disk.
It is an object of the present invention to provide a method of optimizing the read focus of an optical storage system which minimizes media consumption. That is, the process does not utilize large amounts of storage media simply for the read focus optimization process.
It is a further object of the present invention to provide a method and system for carrying out read focus optimization which is relatively fast and efficient.
It is a further object of the present invention to utilize a prewritten track of read focus data which includes predetermined data patterns when carrying out read focus optimization.